The surface treatment of inorganic particles has been addressed over the years by many different techniques and chemical efforts. Some of the techniques are the application of coatings to the surface of particles, using coupling agents on the surface of the particles, physically modifying the surface of the particles, chemically modifying the innate composition on the surface of the particles, and/or modifying the formulation to accommodate the particle—this latter is one of the least desirable methods of controlling particulate behavior in formulation as it limits formulation composition and ingredients and may alter essential formulation and product properties.
The surfaces of zinc oxide and titania have been conventionally coated by adsorption, ion exchange, and covalent bonding. Adsorption and ion exchange require the surface to have the appropriate chemical characteristics. Reactions that enable covalent bonding to particle surfaces generally involve reactions with a surface-bound hydroxyl group. These coatings are thin surface treatments which afford a degree of formulation and product compatibility and for the best available technology no particulate aggregation, but can not prevent ion migration from reactive particles or affect ultimate control of interfacial material properties.